1. Field of the Invention
The present invention generally relates to methods of using poly(arylene ether phosphine oxide)s and, more particularly, to the use of poly(arylene ether phosphine oxide)s in applications requiring a high oxygen plasma or atomic oxygen resistant surface.
2. Description of the Prior Art
High performance engineering thermoplastics have become increasingly important in applications traditionally filled by metallic materials. Moreover, their use in the field of high strength lightweight composite resins has already found many applications in the aerospace, automotive, electronic and related industries. These industrially important thermoplastics include polyesters, polyamides, polyimides and poly (arylene ether)s (PAEs), such as the poly(arylene ether ketone)s (PEKs) and poly(arylene ether sulfone)s (PESs). The latter are tough, rigid thermoplastics with high glass transition, temperatures (T.sub.g s) and/or melting temperatures (T.sub.m s). Another relatively new class of engineering thermoplastics is poly(arylene ether phosphine oxide)s (PEPOs), which may be synthesized by the reaction of bis(4-chlorophenyl)phenyl phosphine oxide (BFPPO) or bis(4-chlorophenyl)methyl phosphine oxide (BFMPO) with bisphenols in various aprotic dipolar solvents utilizing sodium hydroxide or potassium carbonate as the base.
It is also well-known in the art that the presence of phosphorus in PAEs generically imparts flame-retardance to these materials. In addition, compounds such as triphenyl phosphine oxide (TPPO) have been known to be thermally stable at temperatures of up to 700.degree. C., although the study of polymeric materials containing the triphenyl phosphine oxide moiety chemically bound within the polymer chain as flame retardant polymers has been limited. On the other hand, PESs and PEKs have been explored in terms of thermogravimetry of pyrolysis in order to obtain a more detailed analysis of the degradation process. These materials begin to degrade by chain scission at the sulfone or ketone group to give sulfur dioxide or carbon monoxide, respectively. The radicals formed from this initial reaction go on to initiate further chemistry, finally totally volatilizing the polymer at sufficiently high temperatures. Generally, the bonding around phosphorus in these polymers is to oxygen or nitrogen, such as phosphites, phosphonates or phosphazenes. Therefore, in almost all cases, oligomeric forms of these hydrolytically unstable molecules are incorporated as flame-retardant additives and not utilized as homopolymer systems.
In recent years, polyimides and PAEs have become of increasing interest for use in the aerospace industry. More specifically, these polymers have been utilized in space shuttle missions. However, it has been found that these polymers become seriously degraded by atomic oxygen (AO) while in low earth orbit (LEO). In fact, this degradation process, normally called etching, can severely reduce polymeric lifetimes. In efforts to overcome this problem, researchers have focused on developing new materials which are more resistant to O.sub.2 etching. For example, Arnold et al., Miscible Blends of Poly(siloxane Imide) Segmented Copolymers and Polybenzimidazole as Potential High Performance Aerospace Materials, High Performance Polymers, Vol. 2, No. 2, 83 (1990), disclose blends of high performance engineering thermoplastics which exhibit stability in an aggressive AO environment. The blends are comprised of polyimide homopolymers and poly(siloxane imide) segmented copolymers based upon benzophenone tetracarboxylic dianhydride and m-diaminodiphenylsulfone, and polybenzimidazole. Wood et al., Synthesis of New Bismaleimides Derived from Bis(3-amino phenoxy) triphenylphosine oxide and Bis(4-fluoro benzoyl) benzene, 36th International SAMPE Symposium, 1355 (April, 1991), disclose the synthesis of bis(3-maleimido phenoxy) triphenylphosphine oxide (BMPPO) having the following structure: ##STR1## Upon curing, the material demonstrated a T.sub.g of approximately 400.degree. C. and had unusually good fire resistance. The decreased etch rates observed for the materials disclosed by both Arnold et al. have been attributed to the generation of an inorganic, oxidation resistant silicate layer which tends to protect the polymeric underlayer to some extent.